A. Field of the Invention
The invention relates to a sensor for checking value documents and an apparatus for checking value documents, said apparatus containing the sensor.
B. Related Art
For checking value documents usually sensors are used, with which the type of the value documents is determined and/or with which the value documents are checked for authenticity and/or their state. Such sensors are used for checking value documents such as e.g. bank notes, checks, identity cards, credit cards, check cards, tickets, vouchers and the like. The check of the value documents takes place in an apparatus for value document processing which, depending on the value document properties to be checked, contains one or several different sensors. Usually the value documents upon checking are scanned in one or several tracks, whereby the sensor and the value document are moved relative to each other.
The value documents are frequently checked with the aid of optical sensors, which capture the light emanating from the value documents. To illuminate a value document light sources of different colors are used. Usually the light emitted by the light sources is directed onto the value document to be checked directly or with the aid of lenses. However, there is the problem that several different light sources which are disposed in different locations are to illuminate the same region on the value document. With the aid of beam splitters a common beam path for the emission light of the light sources could be achieved; due to the partial transmissivity of the beam splitters, however, a large proportion of the emission light remains unused.
It is also known to use, for illuminating the value document, several light sources of different colors, whose light is directed onto the value document via a common light guide. Due to the relative movement between the sensor and the value document transported past it, however, a minimum distance between the light guide and the sensor is required. Since the light diverges upon exiting from the light guide, this minimum distance results in the illuminated area on the value document being relatively large and the illumination intensity being correspondingly low. Such an illumination is thus unfavorable when the optical properties of a value document are to be captured in a spatially limited region.
It is thus an object of the present invention to supply a sensor for checking value documents which can illuminate largely the same spatially limited region of the value document with the emission light of different light sources.